The present invention relates to a filtering device which is especially designed for use as a well screen filter.
Well bores generally are either vertical or horizontal. Vertical well bores are more commonly known, but in certain applications horizontal wells have several advantages. Especially, horizontal wells may be easily designed with a length of several hundred meters and much more and therefore allow for very large filtering areas.
Details of this horizontal well technology as well as the problems associated therewith may be learned from US 2001/0003313 A1 which is incorporated in its entirety herein by reference.
This reference also describes the problems associated with vertical wells so that again reference may be made to this US patent application for further details of the prior art.
One problem encountered with horizontal as well as the vertical wells originates from the large dimensions of the filtering devices needed. They have to withstand large stresses in axial direction. While conventional filter media used for well screen filters may have a tensile strength of 1 metric ton or somewhat more, which is sufficient to maintain integrity of the filter media once the well screen filter is in place, larger well projects require a tensile strength of 20 metric tons or even more for safe handling of the filtering device during the period of manufacture and especially transporting and positioning of the filtering device within the well bore. In order to cope with such large mechanical forces, use of a tubular casing for the filtering device is required to provide for the necessary tensile strength which, after deposition of the filtering device in the well bore, has to be removed.
However, manufacturing of the casing, positioning of the casing and removing the casing from the well bore requires substantial additional time during which the well drilling equipment is still needed, which causes a substantial increase in costs.
For example, the providing of a horizontal well bore of 300 m length with a filtering device requires approximately one week. If the well bore extends to approximately 15 km, it takes a complete year to provide the well bore with the corresponding filtering device.
The object of the present invention is to provide a filtering device which may be positioned in the well bore with lower costs and which may be easily manufactured and transported to the site of the well bore.